The operational efficiency and the overall output of a gas turbine engine generally increases as the temperature of the hot combustion gas stream increases. Higher combustion gas stream temperatures, however, may produce higher levels of nitrogen oxides and other types of regulated emissions. A balancing act thus exists between the benefits of operating the gas turbine engine in an efficient temperature range while also ensuring that the output of nitrogen oxides and other types of regulated emissions remain below mandated levels. Moreover, varying load levels, transient operations, varying ambient conditions, and many other types of operational parameters also may have a significant impact on overall gas turbine output, efficiency, and emissions.
Lower emission levels of nitrogen oxides and the like may be promoted by providing for good mixing of the fuel stream and the air stream prior to combustion. Such premixing tends to reduce combustion temperature gradients and the output of nitrogen oxides.
There is thus a desire for improved fuel nozzle designs. Such improved fuel nozzle designs may promote good mixing of the flows of fuel and air therein so as to operate at higher temperatures and efficiency but with lower overall emissions and lower dynamics. Moreover, such improved fuel nozzle designs may accomplish these goals without greatly increasing overall system complexity and costs.